pleas take a look at the following image. It shows a strange error with a over sized and kind of corrupted <header> in the site options. It seems like this happens only at the site options pages and even more strangely only at the live server and not when running on my localhost (via MAMAP). Does anyone have an idea what might happen here?

Actually, I have seen this too a couple of days ago with 2.5.10. I am not using that plugin. I couldn’t replicate it and it went away when i restarted my local server. Basically i couldn’t click any buttons, the browser scroll bars disappeared, and all that I could do was slide the whole panel similar to as in your screenshot if I rolled my mouse wheel, except for me the whole page slide and it was white above the toolbar rather then a huge black tool bar.

I would have reported it but there was no point until i had more of an idea of how it happened.

Next time it happens to you see if there is anything in the black bar like an error dump or something. Text is black. If there was an error dump in there it would look bigger, but as text is black it might not have been obvious. I dont know if that is even possible with Kirby but i have had it happen with other CMS systems.